In the paper and board industry, the use of secondary fibres derived from recycling waste paper material is well-known, and the dispersal and separation of ink particles from waste paper material and its secondary fibres is a necessary step in the recycling of the material, particularly in the production of paper for newsprint, tissues, and fine paper.
In known re-cycling processes, the waste paper or "furnish" is usually placed in a hydropulper where it is mixed with water and the following chemicals:
(1) caustic soda or other de-inking chemical, PA1 (2) sodiummetasilicate a buffering agent, and PA1 (3) hydrogen peroxide or other bleaching agent.
In the hydropulper, the "furnish" is disintegrated into a fibrous pulp, which is then de-inked and bleached by the added chemicals. From the hydropulper the fibrous pulp or slushed fibres, with a consistency of 15% (as in high consistency pulping) or 5-6% (as in mills not using high consistency pulping), is dumped into a series of "dump" or storage chests where the slushed fibres are diluted down to a consistency of around 1.5%.
The "stock" or diluted slush fibres then pass to the de-inking equipment, which either consists of flotation cells or washing screens or a combination of these, where the dispersed ink particles are removed from the slushed fibres.
In the method of utilising flotation cells, a "collector" soap is added to the "stock" prior to entering the de-inking cell to agglomerate the dispersed ink-particles which then float to the surface of the cell on air-bubbles which are sourced at the base of the flotation cell and which are then skimmed off.
In the washing method of de-inking, the dispersed ink particles are washed out of the system by passing the stock onto a rotary decker, a sidemill screen, a screw press, or similar equipment, using large volumes of water.
These known methods of de-inking require the addition of a number of different chemicals to achieve the de-inking process which is generally carried out at high temperatures, for example at least 122.degree. F. (50.degree. C.), and under strong alkaline conditions. Some chemicals are also only effective for one of the two different methods, i.e. flotation and washing methods, and cannot be used in the other method. Furthermore, caustic soda, which is most commonly used in relatively large amounts as a de-inking chemical, can attack the fibres and may not be regarded as being envirorunentally safe when emptied from the mill into external water sources.